What are the black, crystal-like protrusions in 1899?

1899 is Netflix’s latest mystery series. From Dark creators Baran bo Odar and Jantje Friese, 1899 promises to enthrall viewers with its twisty narrative and complex puzzles.

Set on a steamship headed to America from England just before the turn of the century, 1899 follows a group of migrants onboard the Kerberos who soon realize that not everyone on the steamship is who they claim to be. Even worse, they stumble upon the missing Prometheus, a ship that went missing four months prior to their departure.

Finding the Prometheus triggers a bizarre chain of events that quickly turns the trip into a nightmare.

Warning: MAJOR spoilers ahead for 1899 on Netflix

As things start going increasingly wrong on the Kerberos, the passengers begin noticing strange, black, crystal-like protrusions appearing all over the ship. What is the black stuff, and is it dangerous?

What are the black, crystal-like protrusions in 1899?

The show doesn’t explicitly go out of its way to tell us what the black stuff is or how it works, but Henry Singleton and Daniel refer to it as the “virus.” The black substance appears to be a physical manifestation of the virus infecting the simulation when it’s about to be deleted.

When Daniel tampers with the console on the ship, he makes the virus much worse and causes it to spread further. At the end of the season, the black stuff, which looks kind of like lead and similar to whatever the black pyramid is made of (and the smaller version Elliot carries around), also becomes increasingly aggressive as the season progresses and the simulation falls apart.

Mrs. Wilson makes the mistake of touching the stuff when it leaks in through a window, and it eats away at her hand, slowly taking over her body before parts of her start disintegrating. It’s similar to what happens to the Kerberos in the season finale when the simulation counts down toward deletion.